Textural complexity

Abstract

The human temporal cortex is known to be involved in visual learning and memory, but its role in visual perception is poorly understood. Studies in macaque monkeys have shown the temporal cortex to have a critical role in complex shape and texture discrimination. Recently, Huxlin and Merigan 1 Huxlin K.R. Merigan W.H. Deficits in complex visual perception following unilateral temporal lobectomy. J. Cogn. Neurosci. 1998; 10: 395-407 Crossref PubMed Scopus (14) Google Scholar tested whether the human temporal cortex is involved in similar tasks by investigating deficits in complex texture- and luminance-based visual discrimination in three patients with temporal lobe lesions. They showed that patient performance (relative to age-matched controls) was specifically affected in tasks involving the perception of texture-based shapes. When shapes were defined by luminance cues, performance was in the normal range or slightly decreased. Interestingly, the discrimination deficits were not restricted to the hemifield contralateral to the lesion site, but occurred equivalently in both visual hemifields. These results are in agreement with data from electrophysiological recordings in monkeys, although the authors emphasize the limited knowledge we have about the homologies between the human and monkey temporal cortex. Finally, it has to be noted that the test of patient performance in object naming based on line drawings did not yield a deficit. This suggests that the temporal lobectomy patients studied in this experiment were impaired only in making subtle visual discriminations, involving complex shapes and/or fine textures. This result is interesting in the light of the localization of the lesions in these patients. Although it is not specifically stated, it seems that their lesions are restricted to the lateral surface of one temporal lobe, mainly in its anterior half. Perhaps this explains the discrepancy between the findings of Huxlin and Merigan in the object naming task and data from visual agnosic patients, whose lesions are usually more ventral and who fail this task. This study proposes that the temporal cortex plays a role in texture-based information processing that may explan its function in specifically complex visual perception.